we could agree to switch to mBTC everywhere (clients, merchants, traders).
This was from November:
...it'll be time for the client to switch to millicoins (e.g. .001 BTC)
Yes it doesn't need to be switched
everywhere, it's just a matter of choosing whatever client software suits you.
Some people will continue to enter '0.05' into their bitcoin client program, while others will decide to run SuperClientmBTC (tm) which takes mBTC as input instead.
Both send the same amount behind the scenes.